The paper industry has been practicing wastepaper recycling to regenerate usable cellulosic fiber for paper making for many decades. In these processes, ink is removed from the wastepaper pulp using a suitable deinking composition. The deinking process produces a new paper or paperboard product out of materials that might otherwise have ended up in a landfill.
Because of increasing public demand, the use of recycled paper has steadily increased. To recover the fibers used for papermaking from wastepaper, a waste paper deinking operation must generally be carried out to remove the inks used in printing, and thus create suitable characteristics for re-use. Traditionally, deinking has been conducted by either washing or flotation deinking.
Wastepaper may contain a mixture of newspapers, magazines, telephone directories, printed advertising material, corrugated containers and the like. The paper fibers used to produce these materials may be chemically pulped materials, such as Kraft pulps, or may be mechanical produced pulps, such as groundwood or mixtures thereof. Much of this wastepaper has undergone some form of printing operation thus leaving a deposit of ink on the paper. To date, wastepaper recycling has concentrated on removal of the ink, prior to re-use of the recycled waste paper for further printing.
The basic stages in a typical washing or flotation deinking process are: repulping the wastepaper in a repulper; coarse cleaning and screening of the repulped material; washing and/or flotation deinking; fine cleaning and screening; post-bleaching, and finally, storage.
A key component in a typical old newspaper (ONP) deinking operation is treatment of the waste paper in the repulper. In the repulper, the wastepaper is typically treated in water with chemicals such as caustic soda, sodium silicate and hydrogen peroxide. A metal chelating additive may also be included.
Repulping is often followed by a series of coarse cleaners and screens to remove large particles, like staples and plastics from the pulp. The cleaned pulp is passed to either a wash or a flotation deinking stage.
Conventionally, two different methods are employed to isolate the ink and ink related entities in order to produce the deinked fiber after repulping. These two processes are flotation and washing. The underlying chemical and physical goals to successfully deink are different for these two methods.
For instance, washing typically requires fine dispersion of ink that is modified to be hydrophilic in nature and thus well dispersed so as to successfully be washed out of the stock thus resulting in the desired separation of ink from the fiber system or deinking. The ink and fiber are more or less uniformly distributed throughout the slurry, and foaming or bubble formation, though present, is not particularly desired. The objective in the washing process is to release and liberate the ink from the fiber into an aqueous medium and then separate the ink and associated entities from the fiber. Thus, the washing method typically comprises repulping, preferably under low-foaming conditions, of secondary fiber in an ink-removing aqueous medium, whereby the ink (and other non-cellulosic contaminants, if present) is mechanically and/or chemically removed as desired depending on the process goals from the fiber. The repulping step is then typically followed by at least a partial change of the aqueous medium, e.g. dilution and/or screening. Wash deinking can occur in the field at pH's lower than 8. This is in part because certain surfactants are known to modify interfacial properties successfully at low pH but these surfactants also modify the ink into a hydrophilic dispersed state that is good for washing but very bad for flotation.
Flotation processes are fundamentally different that washing processes in that the ink may need to be agglomerated following release and liberation for the fiber surfaces. This alteration of ink characteristics can facilitate attachment to air bubbles as well as assists to impart sufficient hydrophobic character to the released and liberated ink and ink related moieties to favor attachment to and stabilization to the air or other gaseous bubbles which is the means of separating the ink from the fiber system. Flotation methods of ink isolation generally involve passing a stream of air bubbles through an aqueous stream of dispersed cellulose fiber (i.e., the repulped cellulose fiber slurry), the cellulose fiber slurry having therein flotation additives, which promote the adhesion of ink particles to the air bubbles. The air bubbles rise within the fiber slurry and carry the ink particles with them thereby generating foam which can be removed from the flotation cell. This method relies upon an unequal distribution of the ink and fiber in the slurrying-flotation medium. Gaseous entities other than air can also be used to generate the bubbles used for flotation during a deinking process that includes one or more flotation steps.
Flotation deinking utilizes a fundamentally different class of surfactants relative to washing because the resulting surface properties are not conducive to washing due to their size distribution and agglomeration states as well as their surface hydrophobicity and lack of dispersion and hydrophilicity that is common for wash deinking. In addition, flotation deinking has historically relied on a high pH pulping liquor to assist in removing ink from the fiber that can then be separated via flotation. This high pH both can also assist in swelling the fibers which may also facilitate ink removal as well as chemically modifying certain points of chemical attachment between the ink and fiber can allow for more efficient ink liberation and release.
Both the washing and flotation processes depend on the proper use of surfactant. Depending on the relative contributions and characteristics of the hydrophilic versus hydrophobic portion of the surfactant molecule, the surfactant will interact in various manners with the ink and other contaminant particles thus rendering the particles hydrophilic for washing purposes or more hydrophobic for flotation. The opposing natures of washing surfactant and flotation surfactant can cause problems in combination flotation/washing systems. The deinking mechanism for washing method is quite different from that for the flotation method and, therefore, they require the use of deinking compositions having different properties.
Typically, either a flotation derived or washing derived deinking chemistry is utilized in a given deinking system. At some point in either process, the deinked, repulped wastepaper is often passed through a series of fine cleaners and/or screens where the small particlulate contaminants, like sand and grit are removed. Additional processing stages may be required, such as for example, dispersion, to reduce the particle size of any contaminants, or a special cleaning stage with special cleaners designed to remove specific contaminants. Further, the repulped wastepaper may also be treated with bleaching chemicals to increase the whiteness and brightness of the pulp.
The deinked wastepaper is then held in storage until it is eventually fed to a papermaking machine. The deinked wastepaper thus provides a furnish of pulp which may be combined with other paper furnishes to eventually produce the saleable paper product.
The chemistry involved in traditional deinking very often involves addition of caustic soda in the repulper to increase the pH. Increasing the pH, however, will often cause yellowing and darkening of the wastepaper stock especially when the wastepaper contains groundwood or mechanical pulps. To counteract the undesirable darkening effect, a bleaching additive is added.
Deinking aids can be solid at room temperature and as such must be heated continually from raw material until use in the mill. This poses a potential problem for clogging lines and shutting down deinking operations.
Accordingly, repulping in a deinking mill might traditionally comprise a repulping unit operation that is conducted at 3.5 to 28% consistency (a term used in the paper industry to describe the concentration (w/v) of an aqueous slurry of pulp fibers), at a pH of 8.8 to 11.5, for 5 to 30 minutes, and at a temperature of 32° C. to 60° C. A typical repulping liquor might comprise additions of the order of 1.5% sodium hydroxide, 3% sodium silicate, and 1% hydrogen peroxide. The treated pulp exiting the repulper is usually dark in color, and is subsequently fed to the wash and/or flotation deinking stage for separation of the ink from the pulp.
The use of a substituted oxyethylene glycol nonionic surfactant along with a low molecular weight polyelectrolyte for deinking secondary fiber is described in U.S. Pat. No. 4,599,190 to Maloney. U.S. Pat. No. 5,094,716 describes a process for deinking groundwood newsprint wherein a combination of certain anionic surfactants in conjunction with a defoamer and a naphthalene-formaldehyde condensate is used.
The removal of electrostatic inks and toners from xerographically printed waste paper has been described for example in U.S. Pat. No. 4,561,733 to Wood, U.S. Pat. No. 4,276,118 to Quick; U.S. Pat. Nos. 4,820,379 and 5,102,500 both to Darlington.
Enzymes have been used in the treatment of paper pulps and for purifying the waste water effluents from paper mill operations. Japanese Pat. Nos. JP 2160984 and JP 2080684 describe the use of the enzyme, lipase, in the hydrolysis of soya-based inks. The use of another enzyme, cellulase, has been described in Japanese patent No. JP 2080683. European patent application No. EP 447672 describes deinking waste paper using a lignolytic enzyme.
U.S. Pat. No. 4,518,459 discloses a deinking method using a deinking composition obtained by adding a predetermined amount of propylene oxide to the terminal hydroxyl groups of alcohols or ethylene oxide adducts of alkylphenols, or by modifying, with benzyl ether, the terminal hydroxyl groups of alcohols or ethylene oxide- or ethylene oxide/propylene oxide block-adducts of alkylphenols.
U.S. Pat. Nos. 3,021,372; 2,856,434; 2,903,486; 3,340,309; 3,444,242 and 3,625,909 disclose compounds which are prepared by adding alkylene oxides to alcohols or alkylphenols.
U.S. Pat. No. 4,162,186 discloses a deinking composition comprising a combination of an oil-soluble alcohol ethoxylate with a water-soluble alcohol ethoxylate.
U.S. Pat. No. 5,094,716 describes the use of a combination of an anionic surfactant and an anionic dispersant for use in removal of hydrophobic inks in wash processes.
U.S. Pat. No. 4,599,190 describes the use of polyelectrolyte dispersants in combination with nonionic surfactants in wash deinking of secondary fiber.
U.S. published application 2003/0106654 A1 discloses the use of alkoxylated fatty alcohols and tryglycerides for deinking.
U.S. Pat. Nos. 5,227,019 and 5,225,046 disclose use of alkoxylated fatty alcohols and fatty acids for deinking.
WO 97/32076 discloses deinking using esterified product of alkloxylated fatty alcohols and fatty acids.
WO 96/31646 discloses the use of alkoxylated fatty alcohols for liberating ink.
U.S. Pat. No. 6,312,559 B1 discloses use of cationic compounds during flotation.
U.S. Pat. No. 5,651,861 discloses use of cationic polymers for deinking waste papers.
U.S. published application No. 2002/0066880 A1 discloses use of a mixture comprising a polyester and two subsequent surfactants.
U.S. Pat. No. 5,801,135 discloses liquid blends of fatty acid and surfactants such as alkoxylated fatty alcohols.
U.S. Pat. No. 5,725,730 also discloses use of fatty acids and alkoxylated fatty alcohols.
U.S. Pat. No. 6,251,220 discloses a deinking method for flotation using alkylene oxide, oil, fat and an alcohol.
Because of the different chemical properties of flotation and washing deinking, there is a need for a method and composition for deinking waste paper suitable for both flotation and washing.
There is also a need for a method and composition for deinking waste paper in non-alkaline or neutral conditions.
There is also a need for a method and composition for deinking waste paper with compositions which are liquid at room temperature.